Multiple sample coincidence counter

ABSTRACT

In a liquid scintillation coincidence counting apparatus, the improvement wherein multiple radioactive samples are analyzed simultaneously using a counting chamber divided into sections by partition means. Each section of the chamber accomodates a sample and is in visual communication with at least two and less than all of the photomultiplier tubes. The coincidence detection system passes electrical pulses only when coincident electrical pulses are received from all of the photomultiplier tubes in visual communication with a single section of the chamber.

United States Patent n91 Laney 1 Mar. 27, 1973 [54] MULTIPLE SAMPLECOINCIDENCE COUNTER [75] Inventor: Barton ll. Laney, Deerfield, Ill.

[73] Assignee: Nuclear-Chicago Corporation, Des

Plaines, lll.

[22] Filed: May 11, 1971 [211 App]. No.: 142,292

[52] US. Cl. ..250/71.5 R, 250/106 SC [51] Int. Cl ..G0lt 1/20 [58]Field of Search ..250/7l.5 R, l06 SC [5 6] References Cited UNITEDSTATES PATENTS 8/1968 Carrel] ..250/7i.5 R 1/1910 Utting ..250/l06 sc x3,539,806 11 1970 Humphrey ..250/71.5R

Primary Examiner-Archie R. Borchelt Attorney-Lowell C. Bergstedt, WalterC. Ramm, Charles H. Thomas, Jr. and Helmuth A. Wegner [57] ABSTRACT In aliquid scintillation coincidence counting apparatus, the improvementwherein multiple radioactive samples are analyzed simultaneously using acounting chamber divided into sections by partition means. Each sectionof the chamber accomodates a sample and is in visual communication withat least two and less than all of the photomultiplier tubes. Thecoincidence detection system passes electrical pulses only whencoincident electrical pulses are received from all of thephotomultiplier tubes in visual communication with a single section ofthe chamber.

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MULTIPLE SAMPLE COINCIDENCE COUNTER This invention relates to animproved liquid scintillation coincidence counting apparatus. Moreparticularly, multiple radioactive samples are analyzed simultaneouslyusing a counting chamber divided into sections by a partition means.Each section of the chamber accomodates a sample and is in visualcommunication with at least two and less than all of the photomultipliertubes. The coincidencedetection system passes electri cal pulses onlywhen coincident electrical pulses are received from all of thephotomultiplier tubes in visual communication with a single isolatedsection of the chamber.

BACKGROUND OF THE INVENTION Liquid scintillation counting devices are inwidespread use for measuring and recording the radioactive properties ofsample specimens. In a liquid scintillating system, a substance,frequently tissue from a biological organism, is liquified either insuspension or in solution and is placed in a small sample vial alongwith a scintillating liquid. The vial is then viewed by twophotomultiplier tubes. If the organism under study has at one timeinjested a quantity of a radioactive substance, traces of thisradioactive substance will be present in the liquified specimen. Thepresence of this radioactive substance causes radioactive events tooccur, such as the emission of beta rays or gamma rays. When these betaor gamma rays strike the active molecules in the scintillatingliquid,the scintillating liquid will emit flashes of light. These light flashesare received by two photomultiplier tubes which generate electricalpulses that are amplified and recorded. A coincidence detection systemallows recordation of electrical pulses from the photomultiplier tubesonly if such pulses occur in coincidence. Such an arrangement largelyeliminates erroneous recordings due to spurious discharges in either ofthe photomultiplier tubes alone.

In the context of laboratory analysis heretofore mentioned, and in otheruses, large numbers of sample vials frequently must be analyzed. Liquidscintillating systems have been devised which automatically convey thevials to an enclosed viewing chamber using an elevator that lowers thevials from a loading station into the viewing chamber. Once analyzed,the sample vials are returned to the loading station by means of theelevator, and the sample chain is advanced one position. Theconventional systems currently in use accomodate only one vial at atime, however. Despite the automatic conveying systems, the timeconsummed in analyzing a large number of samples is still inordinatelylarge. By virtue of the sheer volume of analysis work that must be done,there is a pressing need to reduce the required time necessary toprocess a large number ofsample vials.

SUMMARY Ol THE INVENTION Accordingly, it is an object of the inventionto provide a liquid scintillating coincidence counting system with thecapability of processing a plurality of samples simultaneously. Usingthe technique disclosed herein, two or any larger number of vials may beprocessed simultaneously. This increased volume handling capability isachieved without a complete duplication in the number of photomultipliertubes and associated circuitry required. That is, the number ofphotomultiplier tubes is necessary increased only 50 percent at the most(where only two samples are analyzed simultaneously) when compared witha duplicated system. This savings of time. and expense is achievedthrough the unique interaction of photomultiplier tubes achieved in theapparatus of this invention. Through appropriate conveying andpositioning means, two or any greater number of samples may be analyzedin the time that it takes to analyze one sample (the sample with thelowest count rate) in conventional liquid scintillating countingsystems. The multiple sample counting apparatus disclosed herein hasseveral distinct advantages over duplicate conventional systems. Amongthe advantages in processing a given number of samples are the reducednumber of photomultiplier tubes required; the reduced amount of totalshielding required; the smaller mass of the total processing system; andsharing of sample changing mechanisms and external standard mechanisms.

Another object of a preferred embodiment of this invention is theprovision of a system for detecting and separately registeringaccidentally coincident pulses from the photomultiplier tubes, asreproduced on a statistical basis. These accidentally coincident pulsesdo not reflect actual radioactive events, but instead representaccidentally coincident spontaneous discharges in the photomultipliertubes.

Further objects that are achieved through the use of the preferredembodiments of this present invention include the provision of timecorrection in counting, rejection of coincidence of photomultipliertubes lacking visual communication with a common isolated section, andselective rejection of unanimously coincident photomultiplier tubepulses.

Because the coincidence detection system in a liquid scintillationcounting device can process only one event at a time, subsequentcoincident pulses generated by scintillations occurring within theprocessing time of previous events must necessarily remain unrecorded.Because the coincidence detecting system and the pulse registrationsystem are not duplicated for each sample being analyzed, thesecomponents remain in the processing mode a greater percentage of theanalysis time then do corresponding coincident detection and pulseregistration systems in conventional liquid scintillating devices. Forthis reason it is particularly important to correct the timing mechanismassociated with the liquid scintillating system in order to achieve anaccurate measurement of counts per unit time. This is achieved in apreferred embodiment of the present invention by incorporating a timingdevice and a dead time correcting means into the liquid scintillationcounting device.

Because of the unique construction of the liquid scintillation countingdevice of this invention, there is a contrast in the interpretation ofcoincident pulses from more than two photomultiplier tubes as comparedwith a similar occurrence in conventional liquid scintillationcoincident counting systems. The simultaneous appearance of pulses fromphotomultiplier tubes lacking direct visual communication with a singlesample is an unrecognizable event and the data resulting therefrom maybe disgarded. This is accomplished by the insertion of a coincidenceblocking means between the coincidence detection system and the pulseregistration system. This coincidence blocking means prevents coincidentsignals from photomultiplier tubes lacking visual communication with asingle sample from being recorded. This device may be further modifiedto form a selective blocking means in still a further refinement of theinvention. While it is normally undesirable to record unanimous pulsesor pulses from photomultiplier tubes not directly exposed to a commonsample, a polling of these types of pulses will frequently reveal theprobable origin of the event in question. Moreover, it may be possibleto determine which of the photomultiplier tubes have contributed theerroneous pulses. This situation may arise when a scintillation occursin one of the samples being analyzed. The event may be recorded by thetwo appropriate photomultiplier tubes associated with that sample, butthe scintillation may also be reflected from one of these appropriatephotomultiplier tubes into the photosensitive faces of otherphotomultiplier tubes. In this event, inappropriate photomultipliertubes discharge simultaneously with the appropriate photomultipliertubes. However, the discharges occurring in the inappropriatephotomultiplier tubes are of a much smaller magnitude than those in theappropriate photomultiplier tubes due to the energy lost by thescintillation in being reflected from one photomultiplier tube toanother. The selective blocking means which may be utilized in preferredembodiments of this invention compares the strength of the electricalpulses from the various tubes. If the smallest pulse from one of thephotomultiplier tubes is much smaller than the second smallest pulsefrom any of the other photomultiplier tubes, an event isrecorded ashaving occurred in the samples scanned by the two photomultiplier tubeswhich emitted the strongest pulses. The weaker pulses from the otherphotomultiplier tubes are rejected as crosstalk signals.

As previously discussed, one further feature of this invention is asystem for detectingaccidental coincidences. The number of accidentalcoincidences is statistically determined and recorded on a separatecounting device. Accidental coincidences occur when separate, spuriousdischarges in the photomultiplier tubes, which would otherwise not berecorded, coincide in time and are erroneously recorded as a trueradioactive event. The number of accidental coincidences that occur maybe statistically determined by generating a duplicate signal from aphotomultiplier tube each time the photomultiplier tube discharges. Thisduplicate signal is not processed along with the true signal, but isintroduced at the input of a separate accidental coincidence detectingand pulse registration system. The duplicate signal will ordinarily failto pass through this system for lack of coincidence. However, should aspurious discharge occur in another interconnected photomultiplier tube,and should this spurious discharge coincide within the resolving timewith the duplicate signal, the two signals together will be registeredas an accidental coincidence. From a probability analysis it can be seenthat the number of accidental coincidences registered due to thegeneration of the duplicate pulse is statistically equal to the numberof accidental coincidences registered in the total pulse registrationmeans due to the original pulse. The number of true events may beobtained by merely subtracting the reading of the accidental pulseregister from the reading of the main pulse register, either manually orautomatically. The provision of a system for accidental pulse correctionis particularly valuable in a system such as that disclosed herein wheremore than two photomultiplier tubes are used in the system, since theprobability of accidentally coincident discharges from twophotomultiplier tubes increases with the addition of eachphotomultiplier tube. Similarly, accidental coincidence betweenscintillations in two different samples increases with the number ofsamples and the sample activity.

In a broad aspect this invention is, in a liquid scintillatingcoincidence counting apparatus comprising a counting chamber forreceiving samples to be measured, photomultiplier tubes located adjacentto said chamber for producing electrical pulses responsive to energyreceived from scintillations occurring in the samples, coincidencedetection means coupled to said photomultiplier tubes for passingelectrical pulses when coincident pulses are received from at least twoof said photomultiplier tubes, and pulse registration means connected tosaid coincidence detection means for recording pulses receivedtherefrom. The improvement wherein partition means divide said chamberinto at least two isolated sections and each of said isolated sectionsof said chamber simultaneously accomodates a separate sample and is invisual communication with at least two and less than all of saidphotomultiplier tubes, and said coincidence detection means passeselectrical pulses only when coincident electrical pulses are receivedfrom all of the photomultiplier tubes in visual communication with asingle isolated section of said chamber. If the chamber is divided intotwo sections, three photomultiplier tubes must be used in order toprovide coincidence counting. If any greater number of isolated sectionsare formed, the number of photomultiplier tubes will necessarilyat leastequal the number of isolated sections.

BRIEF DESCRIPTION OF THE DRAWINGS This invention may be more fullyexplained and the preferred embodiments depicted in the accompanyingdrawings in which:

FIG. I is a sectional elevational view taken along the lines 1-1 of aportion of a liquid scintillation counting apparatus illustrated in FIG.2.

FIG. 2 is a sectional plan view taken along the lines 2-2 of a portionof the liquid scintillation counting apparatus of FIG. 1.

FIG. 3 is a view similar to the view of FIG. 1 of an alternativeembodiment of the invention taken along the lines 3-3 of FIG. 4.

FIG. 4 is a sectional plane view taken along the lines 4-4 of FIG. 3.

FIG. 5 is a sectional plan view of a modified form of the inventionillustrated in FIG. 4.

FIG. 6 is a block diagram of the liquid scintillation counting apparatusof FIGS. 1 and 2.

FIG. 7 illustrates in more detail the electrical convnections in theliquid scintillation counting apparatus DETAILED DESCRIPTION OF THEDRAWINGS Referring now to FIGS. 1 and 2 there is shown a portion of abatch sample liquid scintillation counting apparatus. A counting chamberis defined within a housing 41 and is designed to receive vials ofliquid samples to be measured. Partition means 19 is comprised ofvertically extending segments 20, 21, and 22, located atop elevator 30,which divide the counting chamber 10 into isolated sections 23, 24, and25 when elevator 30 is lowered to below the level of chamber 10, as inFIG. 1. The sections 23, 24, and 25 need be isolated only from eachother, and may be open at the top as illustrated in FIG. 1 as long asthe walls 97 of the elevator shaft and the shutter 45 are highly lightabsorbent. Each of the sections 23, 24, and 25 is in visualcommunication with at least two and less than all of the photomultipliertubes 14, 15, and 16. Since the partition means 19 divides the chamber10 into at least three isolated sections, the number of necessaryphotomultiplier tubes equals the number of sections. That is, the liquidscintillation counting apparatus of FIGS. 1 and 2 requires first,second, and third photomultiplier tubes 14, 15, and 16 respectively.Section 23 is in visual communication with photomultiplier tubes 14 and15 while section 24 is in visual communication with photomultipliertubes 15 and 16. Section 25 is in visual communication withphotomultiplier tubes 16 and 14. A coincidence detection means, such asthe coincidence detection means 17 in FIG. 6, passes electrical pulsesupon receipt of coincident electrical pulses from photomultiplier tubes14 and 15 generated in response to a scintillation in sample 11 locatedin section 23 of the enclosed chamber. Similarly, the coincidentdetection means 17 passes electrical signals upon receipt of coincidentelectrical pulses from photomultiplier tubes 15 and 16 in response to ascintillation in sample 13 within section 24, and upon receipt ofcoincident electrical pulses from photomultiplier tubes 16 and 14 inresponse to a scintillation in sample 12 located in section 25. It canbe seen that any two photomultiplier tubes should generate coincidentpulses only when a scintillation occurs in a specific section of thecounting chamber.

A conveyor system comprised of annular cylinders 46 fastened together bylinks 47 moves across the opening of an elevator shaft defined by thewalls 97. Disks 26 are trapped within the cylinders 46 and are draggedalong the upper surface 44 of the scintillation counting device. Eachdisk 26 has a partition means 19 comprised of vertically extendingsegments 20, 21 and 22. Samples 11, 12, and 13 are located between theupright segments as illustrated. At the start of each sample countingcycle a cylinder 46 is sequentially moved into position above theelevator shaft with the elevator 30 in the raised position. The elevator30 is then lowered carrying with it a disk 26 and an associatedpartition means 19. The shutter 45 closes over the elevator 30 when theposition means 19 is clear. When the elevator 30 is lowered, the timingmeans 99 of FIG. 6 allows the pulse registration means to beginrecording scintillation events occurring in samples ll, 12 and 13. Atthe end of the timing cycle, no more events are recorded and theelevator 30 is raised and the shutter means 45 opens to allow upwardpassage of the elevator 30. The disk 26 is again trapped in the cylinder46 from which it was withdrawn, and the conveyor system advances to thenext sequential position. To obviate a tendency for the disk 26 torotate with respect to the photomultiplier tubes during lowering of theelevator, the disk 26 can be slideably keyed to the walls 97 of theelevator shaft, or restrained in position with respect to the upper faceof the elevator 30 in order to insure proper alignment of the chambersections with the photomultiplier tubes.

An alternative embodiment of the elevator and partition means isillustrated in FIG. 8 in which housing 41' defines a chamber locatedbelow the sample conveyor system, as in FIGS. 1 and 2. In the embodimentof FIG. 8, the partition means 19 is comprised of vertically extendingsegments 20, 21, and 22'. These segments each extend into grooves in thewalls 97' of housing 41 and are scaled thereto in the manner illustratedin connection with the segment 22'. The sements 20, 21', and 22 eachextend out into the scintillation counting chamber and meet at thecenter thereof, thereby dividing the chamber into isolated sections asin the embodiment of FIG. 1. The elevator 30' differs from elevator 30in that it is comprised of three separated columnar portions 119, 120,and 121, which are connected to move in tandem so that all of theelevator portions are raised and lowered in unison. Each of the elevatorportions occupies the entire volume of one and only one of the singleisolated chamber sections when the elevator 30' is raised. Each elevatoraccomodates a sample placed thereon, such as the sample 11. When theelevator portions are lowered they pass longitudinally through thechamber sections and position the samples in the chamber sections whenthe elevator 30' is in the fully lowered position as illustrated in FIG.8.

Another alternative form of the invention is illustrated in FIGS. 3 and4. In this embodiment, a liquid scintillation counting chamber housing40 is located above the conveyor system comprised of cylinders 46 joinedtogether by links 47. The scintillation counting chamber is locatedwithin the housing 40 and has vertically extending segments 31, 32, and33 dividing the scintillation counting chamber into isolated sections34, 35, and 36. The photomultiplier tubes 37, 38, and 39 are locatedabove the isolated sections with tube 37 being in view of both sections34- and 36, tube 39 being in view of both sections 34 and 35, and tube38 being in view of both sections 35 and 36. At the start of each samplecounting cycle, a cylinder 46 with a disk 26 having sample vials 11, 12,and 13 positioned thereon, is advanced to a position directly aboveelevator 30. Elevator 30 rises and passes through cylinder 46 carryingthe disk 26 and the sample vials. Shutter 43 opens automatically withthe upward movement of elevator 30, and the elevator 30 rises through avertically extending elevator shaft in housing 40 that communicates withthe scintillation counting chamber. Elevator 30 moves upward to contactthe vertically extending segments 3]., 32, and 33 of the partitionmeans, thereby defining the isolated sections 34, 35, and 36. Thesamples 11, 12, and 13 are thereby positionable in separate isolatedsections 35, 36, and 34 respectively. Electrical pulses are passed andreceived in the scintillation counter as heretofore discussed.

Still another modification of this invention is illustrated in FIG. 5,which in all respects, other than those enumerated, is similar to theembodiment of FIGS. 3

and 4. The partition means 122 of FIG. divides the scintillation countchamber into first and second isolated sections 23' and 24'respectively. First, second, and third photomultiplier tubes 38', 39,and 37' are positioned vertically above the isolated sections. Section23' is in visual communication with photomultiplier tubes 38' and 39'while section 24' is in visual communication with photomultiplier tubes39 and 37'. The coincidence detection means passes electrical pulsesupon receipt of coincident electrical pulses from photomultiplier tubes38' and 39' which are generated in response to a scintillation fromsample 12 in section 23' of the chamber. Similarly, electrical pulsesare passed upon receipt of coincident electrical pulses fromphotomultiplier tubes 39 and 37' generated in response to ascintillation in sample 13' located in section 24' ofthe chamber. It canbe seen that in this embodiment the number of photomultiplier tubes mustexceed the number of samples being analyzed simultaneously. Whenever thechamber is divided into three or more sections, the requisite number ofphotomultiplier tubes need only be equal to the number of isolatedsections.

Various preferred features of electrical processing are also desirablein the liquid scintillation counting apparatus of this invention. Theseare illustrated in FIGS. 6 and 7, which depict the electrical networkused in the embodiment of FIGS. 1 and 2. The electrical pulses from thephotomultiplier tubes 14, 15, and 16 are passed through preamplifiers107, 108, and 106 respectively associated therewith. The pulses arepassed to a coincidence detection means 17 and through a pulse gatingmeans 109 to a dead time correcting means 98. The coincidence detectionmeans 17 is coupled to the photomultiplier tubes for passing electricalpulses only when coincident electrical pulses are received from all ofthe photomultiplier tubes in visual communication with a single isolatedsection of the scintillation counting chamber. A pulse discriminationand registration means 18 is connected to the coincidence detectionmeans 17 for recording pulses received therefrom. While a pulsediscrimination means is not necessary to the operability of thisinvention, it is normally provided in order to define windows" of pulseamplitude within which the most meaningful pulses are most likely tooccur. The pulse discrimination and registration means 18 also includesa scaler or other conventional data outputdevice. v

A coincidence blocking means 48, which in the embodiment illustrated isa triple coincidence blocking means, is interposed between thecoincidence detec-' tion means 17 and the pulse discrimination andregistration means 18 for blocking pulses from the coincidence detectionmeans 17 resulting from pulses received by the coincidence detectionmeans 17 from all of the photomultiplier tubes l4, l5, and 16. As willbe explained in connection with FIG. 7, the coincidence blocking means48 is adapted for selective blocking of pulses received.

The dead-time correcting means 98 is used to correct the scintillationcounting apparatus for scintillations missed when the coincidencedetection means is unavailable for processing new electrical pulses fromthe photomultiplier tubes because it is already engaged in processingprior electrical pulses therefrom. A timing means 99 is connected to thepulse discrimination and registration means 18 for governing the realtime interval within which pulses are received by the pulsediscrimination and registration means 18. The pulse gating means 109detects single or coincidence pulses in any of the photomultiplier tubesand transmits these pulses to the dead time correcting means 98 and thepulse discrimination and registration means 18. The dead time correctingmeans 98 is connected to the timing means 99, the pulse gating means109, and the coincidence detection means 17 and is utilized to preventthe recordation of pulses in the pulse registration means duringprocessing of prior pulses from the photomultiplier tubes. The dead timecorrecting means also corrects the timing means to compensate for thetime elapsed during which recordation of pulses is prevented in thepulse discrimination and registration means 18.

One further feature of the embodiment illustrated is the accidentalcoincidence discrimination means which is connected generally parallelwith the coincidence detection means and is used to separately registerin pulse discrimination and registration means 18, accidentallycoincident pulses from the photomultiplier tubes reproduced on astatistical basis.

A detailed description of the operation of the electrical components isdepicted in FIG. 7. The pulse registration means is comprised in part oftotal scintillation counting AND gates 49, 51, and 53 for each possiblecombination of two photomultiplier tubes. In addition, the pulseregistration means includes similar AND gates 50, 52, and 54 parallelingthe total scintillation counting AND gates and used for countingaccidentally coincident pulses from the photomultiplier tubes. The ANDgates 49 through 54 are only the initial portion of the pulseregistration means. Other pulse registration means also includes ascalar or the output device, which, along with the pulse discriminationmeans, is conventional and therefore not illustrated. The coincidencedetection means has coincidence activated monostable multivibrator means55, 57, and 59 equipped with disabling mechanisms and associated witheach possible combination of two photomultiplier tubes for providinginput signals of predetermined duration to the scintillation countingAND gates. That is, monostable multivibrator 55 is associated withcoincident pulses from tubes 14 and 15 while monostable multivibrator 57is associated with coincident pulses from tubes 15 and 16. Themonostable multivibrator 59 is associated with coincident pulses fromtubes 16 and 14. In a similar fashion, monostable multivibrator 56 foraccidental pulses is associated with accidental coincident pulses fromtubes 14 and 15. Monostable multivibrator 58 is associated withaccidental coincident pulses from tubes 15 and 16 while monostablemultivibrator 60 is associated with accidental coincident pulses fromtubes 16 and 14. The pulse gating means 109 has a pulse detection meanscomprised of an OR gate 64 and an inverted input OR gate 65 fordetecting pulses of either polarity from the photomultiplier tubes.Normally the pulses of the magnitude desired are produced by thephotomultiplier tubes with a positive spike followed by a decayingnegative component, as illustrated in FIG. 7. Forming a part of thepulse gating means 109 and associated with the OR gate 64 is a gatingmonostable multivibrator means 61 having a prevent-start means, and apulse inverting amplifier 62, which serves as a signal inverting means.OR gates 64 and 65, multivibrator means 61, and inverting amplifier 62are connected to all of the photomultiplier tubes 14, 15, and 16, andprovide inhibiting gating pulses of predetermined duration to the totalscintillation counting AND gates 49, 51, and 53. These inhibiting gatingpulses are introduced to allow time for the pulse height analysiscircuitry in pulse discrimination and registration means 18 to function,and terminate prior to the termination of output signals from themultivibrator means 55, 57 and 59. Similarly, inhibiting gating pulsesare provided to the accident counting AND gates 50, 52, and 54. Theseinhibiting gating pulses are of predetermined duration and terminateprior to the termination of the input signals from the multivibratormeans 56, 58, and 60 which are associated with accidental coincidentpulses. The outputs of the total coincidence activated monostablemultivibrator means, 55, 57, and 59, and the outputs of the accidentalcoincidence monostable multivibrator means 56, 58, and 60, as well asthe outputs of OR gate 65 and gating monostable multivibrator means 61are all connected to the inputs of a dead time activating OR gate 101.OR gate 101 has one output to the prevent-start means of multivibratormeans 61. This prevent-start means takes the form of an AND gate 79operated through an output connection from the dead time activating ORgate 101. OR gate 101 also has an output to the dead time correctingmeans comprised of a time control OR gate 100, a reset monostablemultivibrator means 102, and a capacitor 103. The time control OR gate100 has one input lead from the dead time activating OR gate 101 and hasoutputs to the timing means 99 and to the disabling mechanisms on thecoincidence activated monostable multivibrator means 55 through 60. Thereset monostable multivibrator means 102 has an output gating lead tothe time control OR gate 100, and capacitor 103 is connected between thedead time activating OR gate 101 and the reset monostable multivibratormeans 102.

The triple coincidence blocking means has pulse registration inhibitingmeans interposed between the coincidence detection means and the pulseregistration means. The pulse registration inhibiting means is comprisedof a triple coincidence AND gate 66 having inputs from the outputs of atleast two of the total coincidence activated monostable multivibratormeans and having an output leading to inputs to OR gates 112, 113, and114 which serve as enabling gating means. The OR gates 112, 113, and 114all have inverted inputs so that they are always in an enablingcondition unless triple coincidence pulses are simultaneously generatedin photomultiplier tubes 14, 15, and 16. Even ifa triple coincidenceoccurs, one of the OR gates 112, 113, and 114 connected to the totalscintillation counting AND gates 49, 51, and 53 respectively, may beplaced in an enabling condition by the selective blocking modificationto be described later. In any event, if triple coincidence occurs, nomore than one of the OR gates 112, 113, and 114 will be allowed toremain in an enabling condition and at least the other two OR gates willbe switched to a disabling condition. In a like manner triplecoincidence AND gate 69 associated with accidental coincidences isconnected to the outputs of at least two of the accidental coincidenceactivated monostable multivibrators, and enabling OR gates 116, 117, and118 respectively, are connected to the accident counting AND gates 50,52, and 54.

The triple coincidence blocking means is modified for selective blockingin order to detect triple coincidence pulses resulting from reflectionsbetween photomultiplier tubes and to allow the primary coincident pulsesto be recorded while rejecting the third reflected pulse. In this way,coincident pulses on two of the photomultiplier tubes are detected andrecorded dispite the pulse resulting from a light reflection in theother tube, which would otherwise cause all pulses to be rejected asbeing triple coincident. To achieve selective blocking, a differentialamplitude measuring means 67 for measuring the amplitude differencebetween the largest pulse and the intermediate pulse and for measuringthe difference between the intermediate pulse and the smallest pulseproduced by the photomultiplier tubes is connected to all threephotomultiplier tubes. Differential amplitude measuring means 67generates a difference signal proportional to the difference between theintermediate and smallest pulses, and passes this difference signal tocomparator means 111. Comparator means 111 contains a control signal setby control signal adjustment 72 and proportional to a predeterminedminimum difference value which is calculated to distinguish and identifysmall reflected pulses in the presence of primary pulses resulting froma true scintillation. Comparator 111 compares the difference signal frommeasuring means 67 against the control signal set at 72 and, ifappropriate, selectively generates and passes a signal to either theenabling OR gates 112 and 116, OR gates 113 and 117, or OR gates 114 and118. A signal is generated only when the difference signal frommeasuring means 67 is at least as large as the control signal incomparator 111. If

generated, the signal is inverted and passed only to those enabling ORgates connected to the total and accidental monostable multivibratorsassociated with the largest and intermediate pulses from thephotomultiplier tubes. If the difference signal from the measuring means67 is smaller than the control signal set at 72, then no signal ispassed from comparator 111 to any of the enabling OR gates. in thisinstance all of the total enabling OR gates or all of the accidentalenabling OR gates will switch to a disabling condition because of theoccurrence of either a total triple coincidence or an accidental triplecoincidence. For example, if a triple coincidence occurs and the pulsefrom photomultiplier tube 15 results from a reflected scintillation andis much smaller than the pulses from tubes 14 and 16, then signal ispassed from comparator 111 to OR gates 114 and 118, thereby maintainingthese OR gates in an enabling condition and allowing the pulse frommultivibrator 59 to cause a scintillation count to be recorded by ANDgate 53. AND gate 66 causes the other enabling OR gates to switch to adisabling condition and block recordation of pulses by AND gates 49, 50,51, and 52. After each pulse processing, the differential amplitudemeasuring means 67 is reset by reset multivibrator means 102. Pulsedelay means equal to pulse delay means 105, is interposed in the resetline between differential amplitude measuring means 67 and multivibratormeans 102. This is because the timing of the resetting of measuringmeans 67 must be synchronized with the delay introduced by the summingmeans 88, 89, and 90 and the pulse delay means 94, 95, and 96, yet to bedescribed.

Several additional components are also required for accidentalcoincidence pulse registration. These include normal pulse AND gates 73,75, and 77 associated with photomultiplier tubes 14, 15, and 16respectively, and delayed pulse AND gates 74, 76, and 78 associated withphotomultiplier tubes 14, 15, and 16 respectively. The normal pulse ANDgates and the delayed pulse AND gates have outputs respectivelyoperating the total pulse monostable multivibrators and the accidentalpulse monostable multivibrators. First and second input leads 82 and 83respectively gate the normal pulse AND gate 73 and the delayed pulse ANDgate 74 associated with photomultiplier tube 14. Similarly, first andsecond input leads 84 and 85 respectively gate AND gates 75 and 76 whilefirst input lead 86 and second input lead 87 respectively gate AND gates77 and 78. The summing means 88, 89, and 90 are each respectivelyconnected across the first and second input leads from photomultipliertubes 14, 15, and 16. Coincidence detectors 91, 92, and 93 are providedfor each possible combination of two photomultiplier tubes with anoutput from each coincidence detector gating the normal pulse AND gateand the delayed pulse AND gate associated with one of thephotomultiplier tubes. One input is provided to the same coincidencedetector from the summing means associated with that samephotomultiplier tube, and another input is provided to each coincidencedetector from the first input lead of one of the remainingphotomultiplier tubes. That is, coincidence detector 91 gates normalpulse AND gate 73 and delayed pulse AND gate 74 and has one input fromsumming means 88. Summing means 88, and AND gates 73 and 74 are allassociated with photomultiplier tube 14. The other input to coincidencedetector 91 extends from the first input lead 84 of photomultiplier tube15. Similar connections are repeated for each of the other possiblecombination of any two of the photomultiplier tubes. A pulse delay meansis interposed in each of the second input leads between thephotomultiplier tube and the summing means associated therewith. Moreparticularly, pulse delay means 94 is located in second input lead 83between photomultiplier tube 14 and summing means 88; pulse delay means95 is located in second input lead 85 between photomultiplier tube andsumming means 89; and pulse delay means 96 is located in second inputlead 87 between photomultiplier tube 16 and summing means 90. By usingthe same coincidence detection circuitry for both total and accidentalpulses, problems of varying accuracy, thresholds, and balancing in thecircuit components are obviated. As previously mentioned, the OR gate 64and the inverted input OR gate 65 detect single pulses, accidentallycoincident pulses, and total coincident pulses. The monostablemultivibrator 61 operates the signal inverting amplifier 62 associatedwith the pulse registration AND gates 49, 50, 51, 52, 53, and 54.

The operation of the embodiment of the invention depicted in FIG. 7 maybe further illustrated by an analysis of the circuit conditions uponreceipt of different pulses. Normally, coincident input pulses from anytwo photomultiplier tubes are both initially positive going pulses,either one or both of which cause current to pass through OR gate 64. Ifcoincident pulses are generated by photomultiplier tubes 14 and 15 as aresult of a scintillation in sample vial 11 in section 23, the fact thatthe pulses are coincident causes coincidence detector 91 to gate ANDgate 73 and operate monostable multivibrator 55 which in turn insuresthat current eminates from OR gate 101. The output of OR gate 101 gatesAND gate 79, which combined with the input from OR gate 64, begins thecycle of an inhibiting pulse as initiated by monostable multivibrator61. The pulse from multivibrator 61 is passed to pulse invertingamplifier 62 which inverts the pulse thereby creating an inhibitingpulse which prevents the AND gate 49 from passing current for apredetermined period of time. During the time the current is passed fromAND gate 79, monostable multivibrator 61 is prevented from starting thecycle again so that once the timed inhibited condition of the input leadof AND gate 49 has expired, a gating current is returned to that leadand AND gate 49 is in a condition to accept gating pulses on its otherinput leads and thereafter pass current. If coincidence is presentbetween tubes 14 and 15, the monostable multivibrator 55 will generate agating pulse having a longer duration than the inhibit pulse initiatedby monostable multivibrator 61. This will cause AND gate 49 to conductcurrent once the inhibit pulse from multivibrator 61 has expired,assuming, of course, that a triple coincidence has not occurred. Ascintillation count is thereby registered.

Other events are also occurring in other parts of the circuitsimultaneously with the pulse registration. The generation of single orcoincident pulses, as previously mentioned, causes the dead timeactivating OR gate 101 to conduct current. Besides contributing to theactivation of multivibrator 61, OR gate 101 activates OR gate 100 whichprovides a dead time signal for at least the duration of the operatinginterval of multivibrator 61. When the pulses from the photomultipliertubes terminate and there are no longer any inputs to OR gate 101 (whichwill occur no sooner than after the termination of the inhibit signalfrom multivibrator 61 or after the termination of the output signal fromthe coincidence activated multivibrator 55 if there is pulsecoincidence), current will cease to flow to OR gate 100 from OR gate101. When OR gate 101 is turned off at the end of a dead time interval,reset multivibrator 102 is turned on by the discharge of capacitor 103.The output of multivibrator 102 keeps OR gate 100 turned on for theduration of a predetermined reset interval as internally controlledwithin reset multivibrator 102. The length of the reset interval isselected in accordance with the requirements of the pulse heightanalysis circuitry in pulse discrimination and registration means 18,and is provided to insure that all circuit components are ready toanalyze another input pulse. A dead time signal is thus generated forthe total length of the operation of OR gate 101 plus the length of theoperating period of multivibrator 102. The output of OR gate 100prevents the coincidence activated monostable multivibrators 55, 57, and59 from being activated by acting through the disabling mechanismstherein. The output from OR gate 100, after a delay introduced by pulsedelay means 105 similarly deactivates the accident coincidence activatedmonostable multivibrators 56, 58, and 60. it should be noted that thedelay introduced by pulse delay means 105 must be at least as great asthe delay introduced by the pulse delay means 94, 95, and 96. The outputof OR gate 100 is also conducted to the timer to stop the timing means99 from running during the dead time interval in which the circuitry isunavailable to accept new pulses from the photomultiplier tubes.Unavailability of the electrical components to accept pulses duringprocessing of previous pulses need thereby no longer be a source oferror in liquid scintillation coincidence counting.

Upon receipt of triple coincident pulses, the differential amplitudemeasuring means 67 determines the amplitude differences between thepulses received. If a true scintillation occurred in chamber 23, andprimary pulses were initiated by tubes 14 and 15 but a secondary pulseresulting from light reflected from one of the other photomultipliertubes was also produced by tube 16, the differential amplitude measuringmeans 67 will determine the amplitude difference between the largest andintermediate pulses and between the intermediate and smallest pulses.The pulses from tubes 14 and 15 will be nearly equal and will be muchlarger than the pulse from tube 16. Assuming that the pulse from tube 14is slightly larger than that from tube 15, the differential am plitudemeasuring means 67 will generate a difference signal proportional to thedifference between pulses from tubes 15 and 16. If the amplitudedifference is large, as it will be when one of the signals, such as thesignal from tube 16, is a result of a light reflection, the differencesignal produced will be larger than a predetermined control signal setat 72 in comparator 111. A signal will be generated by comparator 111and this signal will be inverted and passed to the enabling OR gatesassociated with coincidences between the tubes generating the twolargest pulses. In this example, the signal will be passed fromcomparator 111 to the enabling OR gates 112 and 116. This signal willcause OR gates 112 and 116 to remain in an enabling condition while ORgates 113 and 114 will switch to a disabling condition if a triplecoincidence occurs in the pulses generated by tubes 14, 15, and 16.Similarly, OR gates 117 and 1 18 will be placed in a disabling mode if atriple coincidence occurs as detected by accident coincidence activatedmonostable multivibrators 56, 58, and 60. If, on the other hand, thedifference signal from differential measuring means 67 is smaller thanthe control signal, comparator 111 will generate no signals and the ORgates 112, 113, and 114 will be switched to a disabling condition by thedetection of the triple coincidence as transmitted by AND gate 66. ANDgate 66 will be in a conducting state since, if a triple coincidenceoccurs, both of the multivibrators 57 and 59 will be conducting, therebyactivating AND gate 66. Similarly, AND gate 69 will be activated bymultivibrators 58 and 60 if an accidental coincidence occurs and the ORgates 116, 117 and 118 will switch to a disabling mode. lt can be seenthat the total triple coincidence AND gate 66 could be connected to anytwo or all of the total coincidence activated monostable multivibrators55, 57, and 59. Similarly, accident triple coincidence AND gate 69 canbe connected to any two or more of the accident coincidence activatedmultivibrators 56, 58, and 60.

The operation of the accidental coincidence detection feature may befurther explained by referring back to the situation where ascintillation occurred in the sample vial 11 in section 23, andcoincident pulses were produced by photomultiplier tubes 14 and 15. Thepulse from tube 14 passes through first and second input leads 82 and 83to summing means 88. The out put of summing means 88 includes two pulsesfor every pulse received from photomultiplier tube 14. These pulses aresequentially arranged in time because of the delay introduced by thepulse delay means 94 in the pulse passing through the second input lead83. Pulse delay means 94 should be chosen so as to introduce a delaywhich will not coincide with the delay inherent in normal after-pulsingin existing photomultiplier tubes, for an improper choice will result inthe recordation of an inordinately large number of after-pulses ratherthan the random spurious pulses desired. Pulse delay means 94,therefore, should introduce a delay less than about 200 nanoseconds orgreater than about 2 microseconds in order to avoid the ordinaryafter-pulsing period. The sequential pulses generated by summing means88 pass from summing means 88 to coincidence detector 91. Thecoincidence detector 91 is activated by the first pulse from summingmeans 88 and by the coincident pulse from tube 15 conducted via firstinput lead 84 to coincidence detector 911. The output of coincidencedetector 91 coincides with the pulse from tube 14 on first input lead82. These two pulses activate AND gate 73 which initiates the timedpulse on monostable multivibrator 55. This results in an output countingpulse from AND gate 49. as previously described. When the second pulsefrom summing means 88 arrives at coincidence detector 91, the accidentcoincidence activated multivibrator 56 will be operated only if there isan output from coincidence detector 91. This will occur only if a singlestray pulse is generated by tube 15 after the original coincident pulsesfrom tubes 14 and 15, and only if this stray pulse accidentallycoincides in time with the second pulse from summing means 88. In thisinstance, AND gate 74 will be gated and accidental coincidence activatedmultivibrator 56 will generate a pulse and an accident count will beregistered at AND gate 50 as previously described. It will be apparentthat from a probability standpoint it is just as likely that a strayaccidental unrelated pulse will be generated by tube 15 to coincide withthe first pulse eminating from summing means 88 and appearing at ANDgate 73 as it is for such a pulse to coincide with the duplicate pulseeminating from summing means 88. While the probability of the occurrenceof these accidentally coincident events are the same, they are recordeddifferently. In the first instance, the unrelated pulses in tubes 14 and15 are mistakenly identified as a scintillation and recorded at AND gate49. In the second instance, however, the pulses are recognized as beingonly accidentally coincident and are registered at AND gate 50. Theoutput of AND gate 49, therefore, should be considered to berepresentative of the total sum of actual scintillations andaccidentally coincident pulses. The output of AND gate 50 should then beconsidered as representative of only accidental pulses. The total actualscintillations may be computed merely by subtracting the count of ANDgate 50 from that of AND gate 49. This subtraction may be made eitherautomatically or manually.

The detailed descriptions and illustrations of the preferred embodimentsdepicted herein have been given for purposes of illustration only, andno unnecessary limitations should be construed therefrom. For example,conventional electrical components may be substituted for those depictedherein to carry out the essential functions of this invention. Moreover,other embodiments and utilizations will be apparent to those familiarwith the field of this invention. For example, external standardizationmay be employed using the multisample simultaneous analysis describedherein. Also, it will be apparent that corresponding circuit conditionswill exist where coincidence occurs between pulses from tubes 15 and 16or tubes 16 and 14, rather than the coincidence between pulses fromtubes 14 and 15 as described in connection with the illustrations.

It will be obvious to those familiar with liquid scintillationcoincidence counting that programmable digital equipment can besubstituted for much of the analogue circuitry depicted in the diagrams.For example, the selective blocking means depicted in the drawings couldvery easily be constructed in the form of programmable digitalequipment.

I claim as my invention 1. In a liquid scintillation coincidencecounting apparatus comprising a counting chamber for receiving samplesto be measured, photomultiplier tubes located adjacent to said chamberfor producing electrical pulses responsive to energy received fromscintillations occurring in the samples, coincidence detection meanscoupled to said photomultiplier tubes for passing electrical pulses whencoincident pulses are received from at least two of said photomultipliertubes, and pulse registration means connected to said coincidencedetection means for recording pulses received therefrom, the improvementwherein partition means divide said chamber into at least two isolatedsections and each of said isolated sections of said chambersimultaneously accomodates a separate sample and is in visualcommunication with at least two and less than all of saidphotomultiplier tubes, and said coincidence detection means passeselectrical pulses only when coincident electricalpulses are receivedfrom all of the photomultiplier tubes in visual communication with asingle isolated section of said chamber.

2. The liquid scintillation counting apparatus of claim 1 furthercharacterized in that said partition means divides said chamber intofirst and second isolated sections, and said first section is in visualcommunication with first and second photomultiplier tubes, and saidsecond section is in visual communication with said secondphotomultiplier tube and a third photomultiplier tube, and saidcoincidence detection means passes electrical pulses upon receipt ofcoincident electrical pulses from said first and second photomultipliertubes generated in response to a scintillation from a sample in saidfirst section of the said chamber and upon receipt of coincidentelectrical pulses from said second andthird photomultiplier tubesgenerated in response to a scintillation from a sample in said secondsection of said chamber.

3. The liquid scintillation counting apparatus of claim 1 wherein saidpartition means divides said chamber into a predetermined number ofisolated sections, and the same number of photomultiplier tubes are invisual communication with said sections and each photomultiplier tube isin visual communication with each of two different sections, and each ofsaid sections is in visual communication with two differentphotomultiplier tubes.

4. The liquid scintillation counting apparatus of claim 3 wherein acoincidence blocking means is interposed between said coincidencedetection means and said pulse registration means for blocking pulsesfrom said coincidence detection means resulting from pulses received bythe coincidence detection means from photomultiplier tubes lackingvisual communication with a common isolated section.

5. The liquid scintillation counting apparatus of claim 3 wherein saidpartition means divides said chamber into first, second, and thirdsections, and said first section is in visual communication with firstand second photomultiplier tubes, said second section is in visualcommunication with said second photomultiplier tube and a thirdphotomultiplier tube, and said third section is in visual communicationwith said third and first photomultiplier tubes, and said coincidencedetection means passes electrical pulses upon receipt of coincidentelectrical pulses from said first and second photomultiplier tubesgenerated in response to a scintillation from a sample in said firstsection, upon receipt of coincident electrical pulses from said secondand third photomultiplier tubes in response to a scintillation from asample in said second section, and upon receipt of coincident electricalpulses from said third and first photomultiplier tubes in response to ascintillation from a sample in said third section.

6. The liquid scintillation counting apparatus of claim 5 wherein atriple coincidence blocking means is interposed between said coincidencedetection means and said pulse registration means for blocking pulsesfrom said coincidence detection means resulting from pulses received bysaid coincidence detection means from all three of the photomultipliertubes.

7. The liquid scintillation counting apparatus of claim 6 wherein:

a. said pulse registration means is comprised of a scintillationcounting AND gate for each possible combination of two photomultipliertubes,

. said coincidence detection means has coincidence activated monostablemultivibrator means associated with each possible combination of twophotomultiplier tubes for providing input signals of predeterminedduration to said scintillation counting AND gates,

. a pulse detection means and signal inverting means are connected toall of said photomultiplier tubes and provide inhibiting gating pulsesof predetermined duration to said scintillation counting AND gates, andsaid inhibiting pulses terminate prior to the termination of said inputsignals,

. enabling gating means normally in an enabling condition connected tothe inputs of said scintillation counting AND gates, and

. said triple coincidence blocking means is comprised of a triplecoincidence AND gate having inputs connected to the outputs of at leasttwo of said coincidence activated monostable multivibrator means andhaving an output leading to an input of the aforesaid enabling gatingmeans for switching said enabling gating means to a disabling condition.

8. The liquid scintillation counting apparatus of claim 6 furthercharacterized in that said triple coincidence blocking means is modifiedfor selective blocking and has differential amplitude measuring meansfor measuring the amplitude difference between the largest andintermediate pulses and between the intermediate and smallest pulsesproduced by said photomultiplier tubes and for generating a differencesignal proportional to the difference between the aforesaid intermediateand smallest pulses, and comparator means for comparing said differencesignal against a control signal proportional to a predetermined minimumdifference value and for selectively passing signals to said means forallowing said enabling gating means to block those pulses from saidcoincidence detection means that result from pulses from all three ofthe photomultiplier tubes where the aforesaid difference signal is lessthan said control signal, and for passing that pulse from saidcoincident detection means that results from the largest andintermediate pulses from the photomultiplier tubes where the aforesaiddifference signal is at least as large as said control signal.

9. The liquid scintillation counting apparatus of claim 1 furthercomprising an accidental coincidence discrimination means for separatelyregistering, in said pulse registration means, accidentally coincidentpulses from said photomultiplier tubes reproduced on a statisticalbasis.

10. The liquid scintillation counting apparatus of claim 9 wherein:

a. three photomultiplier tubes are utilized,

b. said pulse registration means is comprised of a total scintillationcounting AND gate and an accident counting AND gate for each possiblecombination of two photomultiplier tubes,

c. separate coincidence activated monostable multivibrator means fortotal pulses and for accidental pulses are associated with each possiblecombination of two photomultiplier tubes for providing input signals tosaid total scintillation counting and accident counting AND gatesrespectively in response to coincident pulses,

a normal pulse AND gate and a delayed pulse AND gate associated witheach photomultiplier tube have outputs operating a total pulsemonostable multivibrator and an accidental pulse monostablemultivibrator respectively,

e. first and second input leads from each photomultiplier tuberespectively gate said normal pulse AND gate and said delayed pulse ANDgate,

f. a summing means is connected across the first and second input leadsfrom each photomultiplier tube,

. coincidence detectors are provided for each possible combination ofany two photomultiplier tubes with an output from a coincidence detectorgating the normal pulse AND gate and the delayed pulse AND gateassociated with one of the photomulscintillation counting AND gates andsaid accident counting AND gates.

11. A batch sample liquid scintillation counting apparatus comprising:

a. a housing defining a counting chamber for receiving samples to bemeasured,

b. photomultiplier tubes located adjacent to said chamber for producingelectrical pulses responsive to energy received from scintillationsoccurring in the samples to be measured,

c. partition means dividing said chamber into a plurality of isolatedsections, each section accomodating a sample, and each section being invisual communication with at least two and less than all of saidphotomultiplier tubes,

d. coincidence detection means coupled to said photomultiplier tubes forpassing electrical pulses only when coincident electrical pulses arereceived from all of the photomultiplier tubes in visual communicationwith a single isolated section of said chamber, and

e. pulse registration means connected to said coincidence detectionmeans for recording pulses received therefrom.

12. The batch sample liquid scintillation counting apparatus of claim 11wherein said partition means is comprised of vertically extendingsegments located atop an elevator, and said elevator accomodates samplespositioned between said partition segments which divide said chamberinto sections when said elevator is lowered to below the level of saidchamber.

13. The batch sample liquid scintillation counting apparatus of claim 11wherein said partition means is comprised of vertically extendingsegments sealed to said housing and extending into said chamber, anddividing said chamber into the aforesaid isolated sections and saidelevator is comprised of separated columnar portions movable in tandumeach fully occupying a single isolated section when said elevator israised and each accomodating a sample placed atop thereof forpositioning in said isolated sections of said chamber when said elevatoris lowered.

14. The batch sample liquid scintillation counting apparatus of claim 11wherein said partition means is comprised of vertically extendingsegments, and said chamber has a vertically extending elevator shaft incommunication therewith, and an elevator accomodates samples positionedthereon and is movable upward to contact said vertically extendingsegments, thereby defining the aforesaid isolated sections, wherebysamples positioned atop said elevator are positionable in separateisolated sections of said chamber.

15. The batch sample liquid scintillation counting apparatus of claim 11further comprising a timing means connected to said pulse registrationmeans for determining the time interval within which pulses are receivedby said pulse registration means, and a pulse gating means is connectedto all of said photomultiplier tubes, and a dead time correcting meansis connected to said timing means, said pulse gating means, and saidcoincidence detection means for temporarily preventing the recordationof pulses in said pulse registration means during processing of priorpulses from said photomultiplier tubes, and for correcting said timingmeans to compensate for the time elapsed during which recordation ofpulses is prevented.

16. The batch sample liquid scintillation counting apparatus of claim 14further characterized in that:

a. said pulse registration means is comprised of scintillation countingAND gates for each possible combination of two photomultiplier tubes,

b. said coincidence detection means has coincidence activated monostablemultivibrator means equipped with disabling mechanisms associated witheach possible combination of two photomultiplier tubes for providinginput signals of predetermined duration to said pulse registrationmeans,

0. a dead time activating OR gate is additionally connected to theoutputs of said coincidence activated monostable multivibrator means,

d. said pulse gating means is further comprised of: (i)

pulse inverting means for providing inhibiting gating pulses ofpredetermined duration to said scintillation counting AND gates and saidinhibiting pulses terminate one input lead from said dead timeactivating OR gate and with outputs to said timing means and saiddisabling mechanisms of said coincidence activated monostablemultivibrator means, (ii) a reset monostable multivibrator means havingan output gating lead to said time control or gate, and (iii) acapacitor connected between said dead time activating OR gate and saidreset monostable multivibrator means.

1. In a liquid scintillation coincidence counting apparatus comprising acounting chamber for receiving samples to be measured, photomultipliertubes located adjacent to said chamber for producing electrical pulsesresponsive to energy received from scintillations occurring in thesamples, coincidence detection means coupled to said photomultipliertubes for passing electrical pulses when coincident pulses are receivedfrom at least two of said photomultiplier tubes, and pulse registrationmeans connected to said coincidence detection means for recording pulsesreceived therefrom, the improvement wherein partition means divide saidchamber into at least two isolated sections and each of said isolatedsections of said chamber simultaneously accomodates a separate sampleand is in visual communication with at least two and less than all ofsaid photomultiplier tubes, and said coincidence detection means passeselectrical pulses only when coincident electrical pulses are receivedfrom all of the photomultiplier tubes in visual communication with asingle isolated section of said chamber.
 2. The liquid scintillationcounting apparatus of claim 1 further characterized in that saidpartition means divides said chamber into first and second isolatedsections, and said first section is in visual communication with firstand second photomultiplier tubes, and said second section is in visualcommunication witH said second photomultiplier tube and a thirdphotomultiplier tube, and said coincidence detection means passeselectrical pulses upon receipt of coincident electrical pulses from saidfirst and second photomultiplier tubes generated in response to ascintillation from a sample in said first section of the said chamberand upon receipt of coincident electrical pulses from said second andthird photomultiplier tubes generated in response to a scintillationfrom a sample in said second section of said chamber.
 3. The liquidscintillation counting apparatus of claim 1 wherein said partition meansdivides said chamber into a predetermined number of isolated sections,and the same number of photomultiplier tubes are in visual communicationwith said sections and each photomultiplier tube is in visualcommunication with each of two different sections, and each of saidsections is in visual communication with two different photomultipliertubes.
 4. The liquid scintillation counting apparatus of claim 3 whereina coincidence blocking means is interposed between said coincidencedetection means and said pulse registration means for blocking pulsesfrom said coincidence detection means resulting from pulses received bythe coincidence detection means from photomultiplier tubes lackingvisual communication with a common isolated section.
 5. The liquidscintillation counting apparatus of claim 3 wherein said partition meansdivides said chamber into first, second, and third sections, and saidfirst section is in visual communication with first and secondphotomultiplier tubes, said second section is in visual communicationwith said second photomultiplier tube and a third photomultiplier tube,and said third section is in visual communication with said third andfirst photomultiplier tubes, and said coincidence detection means passeselectrical pulses upon receipt of coincident electrical pulses from saidfirst and second photomultiplier tubes generated in response to ascintillation from a sample in said first section, upon receipt ofcoincident electrical pulses from said second and third photomultipliertubes in response to a scintillation from a sample in said secondsection, and upon receipt of coincident electrical pulses from saidthird and first photomultiplier tubes in response to a scintillationfrom a sample in said third section.
 6. The liquid scintillationcounting apparatus of claim 5 wherein a triple coincidence blockingmeans is interposed between said coincidence detection means and saidpulse registration means for blocking pulses from said coincidencedetection means resulting from pulses received by said coincidencedetection means from all three of the photomultiplier tubes.
 7. Theliquid scintillation counting apparatus of claim 6 wherein: a. saidpulse registration means is comprised of a scintillation counting ANDgate for each possible combination of two photomultiplier tubes, b. saidcoincidence detection means has coincidence activated monostablemultivibrator means associated with each possible combination of twophotomultiplier tubes for providing input signals of predeterminedduration to said scintillation counting AND gates, c. a pulse detectionmeans and signal inverting means are connected to all of saidphotomultiplier tubes and provide inhibiting gating pulses ofpredetermined duration to said scintillation counting AND gates, andsaid inhibiting pulses terminate prior to the termination of said inputsignals, d. enabling gating means normally in an enabling conditionconnected to the inputs of said scintillation counting AND gates, and e.said triple coincidence blocking means is comprised of a triplecoincidence AND gate having inputs connected to the outputs of at leasttwo of said coincidence activated monostable multivibrator means andhaving an output leading to an input of the aforesaid enabling gatingmeans for switching said enabling gating means to a disabling condition.8. The liquid sciNtillation counting apparatus of claim 6 furthercharacterized in that said triple coincidence blocking means is modifiedfor selective blocking and has differential amplitude measuring meansfor measuring the amplitude difference between the largest andintermediate pulses and between the intermediate and smallest pulsesproduced by said photomultiplier tubes and for generating a differencesignal proportional to the difference between the aforesaid intermediateand smallest pulses, and comparator means for comparing said differencesignal against a control signal proportional to a predetermined minimumdifference value and for selectively passing signals to said means forallowing said enabling gating means to block those pulses from saidcoincidence detection means that result from pulses from all three ofthe photomultiplier tubes where the aforesaid difference signal is lessthan said control signal, and for passing that pulse from saidcoincident detection means that results from the largest andintermediate pulses from the photomultiplier tubes where the aforesaiddifference signal is at least as large as said control signal.
 9. Theliquid scintillation counting apparatus of claim 1 further comprising anaccidental coincidence discrimination means for separately registering,in said pulse registration means, accidentally coincident pulses fromsaid photomultiplier tubes reproduced on a statistical basis.
 10. Theliquid scintillation counting apparatus of claim 9 wherein: a. threephotomultiplier tubes are utilized, b. said pulse registration means iscomprised of a total scintillation counting AND gate and an accidentcounting AND gate for each possible combination of two photomultipliertubes, c. separate coincidence activated monostable multivibrator meansfor total pulses and for accidental pulses are associated with eachpossible combination of two photomultiplier tubes for providing inputsignals to said total scintillation counting and accident counting ANDgates respectively in response to coincident pulses, d. a normal pulseAND gate and a delayed pulse AND gate associated with eachphotomultiplier tube have outputs operating a total pulse monostablemultivibrator and an accidental pulse monostable multivibratorrespectively, e. first and second input leads from each photomultipliertube respectively gate said normal pulse AND gate and said delayed pulseAND gate, f. a summing means is connected across the first and secondinput leads from each photomultiplier tube, g. coincidence detectors areprovided for each possible combination of any two photomultiplier tubeswith an output from a coincidence detector gating the normal pulse ANDgate and the delayed pulse AND gate associated with one of thephotomultiplier tubes and with one input to the same coincidencedetector from the summing means associated with that samephotomultiplier tube and with another input to the same coincidencedetector from the first input lead of one of the other photomultipliertubes, h. a pulse delay means interposed in each of said second inputleads between the photomultiplier tube and the summing means associatedtherewith, and i. pulse gating means for detecting pulses in saidphotomultiplier tubes and for gating said total scintillation countingAND gates and said accident counting AND gates.
 11. A batch sampleliquid scintillation counting apparatus comprising: a. a housingdefining a counting chamber for receiving samples to be measured, b.photomultiplier tubes located adjacent to said chamber for producingelectrical pulses responsive to energy received from scintillationsoccurring in the samples to be measured, c. partition means dividingsaid chamber into a plurality of isolated sections, each sectionaccomodating a sample, and each section being in visual communicationwith at least two and less than all of said photomultiplier tubes, d.coincidence detection means coupLed to said photomultiplier tubes forpassing electrical pulses only when coincident electrical pulses arereceived from all of the photomultiplier tubes in visual communicationwith a single isolated section of said chamber, and e. pulseregistration means connected to said coincidence detection means forrecording pulses received therefrom.
 12. The batch sample liquidscintillation counting apparatus of claim 11 wherein said partitionmeans is comprised of vertically extending segments located atop anelevator, and said elevator accomodates samples positioned between saidpartition segments which divide said chamber into sections when saidelevator is lowered to below the level of said chamber.
 13. The batchsample liquid scintillation counting apparatus of claim 11 wherein saidpartition means is comprised of vertically extending segments sealed tosaid housing and extending into said chamber, and dividing said chamberinto the aforesaid isolated sections and said elevator is comprised ofseparated columnar portions movable in tandum each fully occupying asingle isolated section when said elevator is raised and eachaccomodating a sample placed atop thereof for positioning in saidisolated sections of said chamber when said elevator is lowered.
 14. Thebatch sample liquid scintillation counting apparatus of claim 11 whereinsaid partition means is comprised of vertically extending segments, andsaid chamber has a vertically extending elevator shaft in communicationtherewith, and an elevator accomodates samples positioned thereon and ismovable upward to contact said vertically extending segments, therebydefining the aforesaid isolated sections, whereby samples positionedatop said elevator are positionable in separate isolated sections ofsaid chamber.
 15. The batch sample liquid scintillation countingapparatus of claim 11 further comprising a timing means connected tosaid pulse registration means for determining the time interval withinwhich pulses are received by said pulse registration means, and a pulsegating means is connected to all of said photomultiplier tubes, and adead time correcting means is connected to said timing means, said pulsegating means, and said coincidence detection means for temporarilypreventing the recordation of pulses in said pulse registration meansduring processing of prior pulses from said photomultiplier tubes, andfor correcting said timing means to compensate for the time elapsedduring which recordation of pulses is prevented.
 16. The batch sampleliquid scintillation counting apparatus of claim 14 furthercharacterized in that: a. said pulse registration means is comprised ofscintillation counting AND gates for each possible combination of twophotomultiplier tubes, b. said coincidence detection means hascoincidence activated monostable multivibrator means equipped withdisabling mechanisms associated with each possible combination of twophotomultiplier tubes for providing input signals of predeterminedduration to said pulse registration means, c. a dead time activating ORgate is additionally connected to the outputs of said coincidenceactivated monostable multivibrator means, d. said pulse gating means isfurther comprised of: (i) pulse inverting means for providing inhibitinggating pulses of predetermined duration to said scintillation countingAND gates and said inhibiting pulses terminate one input lead from saiddead time activating OR gate and with outputs to said timing means andsaid disabling mechanisms of said coincidence activated monostablemultivibrator means, (ii) a reset monostable multivibrator means havingan output gating lead to said time control or gate, and (iii) acapacitor connected between said dead time activating OR gate and saidreset monostable multivibrator means.